Crest 3D Whitestrips Supreme Flexfit Teeth Whitening Kit, 42 Strips- NWT Lasts 18 months and beyond Use once a day for 1 hour. Our whitest white for a multi-dimensional smile. Exclusive Flex Fit technology design stretches and molds to custom fit your unique smile. Advanced Seal Technology's no slip grip stays put so you can talk and drink water while whitening teeth. Note : Storing Crest 3D White Whitestrips in a refrigerator is fine, however, storing product in a freezer is not recommended